The present invention relates generally to fiber optic sensing devices, and more particularly, to a fiber optic sensing device for detecting multiple parameters in an environment or element, for example. Indeed, the present invention provides advantages related to the use of fiber optic sensing devices in harsh environments, for instance.
Various sensing devices are known and are generally in use. For example, thermocouples are used for measuring the temperature in components of a device, such as exhaust systems, combustors, compressors and so forth. Yet other sensing systems are employed to detect physical parameters such as, strain or temperature in an infrastructure. As one example, Bragg grating sensors are often employed. However, such conventional sensing devices are limited by the operational conditions in which they may be employed. For example, conventional sensing devices are often limited to relatively mild temperature conditions and, as such, limited operational temperature ranges. Indeed, conventional devices are limited to temperatures between +80° C. to +250° C., depending upon the fiber grating coating materials.
As such, it is difficult to measure temperatures for components in high-temperature environments like turbines and engines. Further, for large components, a relatively large number of discrete thermocouples may be required to map the temperatures. Such discrete thermocouples may not be scalable to meet a desired spatial resolution that is generally beneficial for accurate thermal mapping of system components, which can then used to control and optimize the operation of such systems with the objectives of improving efficiency and output. A more accurate and improved spatial resolution thermal mapping is necessary to control such systems (gas turbines, steam turbines, coal-fired boilers, etc.) with more accuracy and fidelity to meet requirements such as better efficiency and output. The sensing devices for gas components such as NOx, CO and O2 also have a similar limitation in terms of accuracy and spatial resolution. A more accurate and spatially dense gas sensing would facilitate more effective and efficient emissions control for gas turbines and coal-fired boilers.
Accordingly, conventional sensing devices present limitations when employed in high temperature and/or harsh environments such as, gas/steam turbine exhausts, coal-fired boilers, aircraft engines, downhole applications and so forth. For example, conventional Bragg grating sensors employ a doped or chemical grating that breaks down in high temperature settings (e.g., a gas turbine exhaust that may reach temperatures of 600° C. or higher).
Certain other conventional systems employ Bragg grating sensors for measuring and monitoring a parameter in an environment. Such sensors utilize a wavelength encoding within a core of the sensor to measure a parameter based upon a Bragg wavelength shift that is generated on illumination of the grating through an illumination source. Thus, environmental effects on the periodicity of the grating alters the wavelength of light reflected, thereby providing an indication of the environmental or elemental effect, such as, temperature or strain, for example. However, it is difficult to simultaneously detect multiple parameters, such as temperature and gas, through a single conventional Bragg grating sensing element. Further, multiple spectral signals at different wavelengths may be required to separate the effect of multiple sensed parameters from one another. Such separation of sensed parameters is conventionally a difficult and time-consuming process.
In certain conventional sensor systems, an additional grating element encapsulated in a different material is placed in series with an existing grating element for separating the effects of two different parameters, such as temperature and strain. Moreover, such systems require overwriting gratings at the same fiber location, which often present difficulties during the manufacturing the fiber grating for the sensor. In summary, conventional Bragg grating sensors do not facilitate discernment of what environmental or elemental factor influenced the sensor, rather only the physical changes in the sensor itself are readily detectable.
Therefore, there is a need for improved sensing devices.